In an experimental study of the transmissibility of BSE to the pig, seven o
f 10 pigs, infected at 1-2 weeks of age by multiple-route parenteral inocul
ation with a homogenate of bovine brain from natural BSE cases developed le
sions typical of spongiform encephalopathy. The lesions consisted principal
ly of severe neuropil vacuolation affecting most areas of the brain, but ma
inly the forebrain. In addition, some vacuolar change was identified in the
rostral colliculi and hypothalamic areas of normal control pigs. PrP accum
ulations were detected immunocytochemically in the brains of BSE-infected a
nimals. PrP accumulation was sparse in many areas and its density was not o
bviously related to the degree of vacuolation. The patterns of PrP immunola
belling in control pigs differed strikingly from those in the infected anim
als.